The construction sector remains one of the most inefficient and unsustainable industries, due in part to the chronic failure to learn from past projects. Within infrastructure contracting, learning is further hampered by project isolation, staff shortages, and commercial pressures. These conditions make it difficult to evaluate past performance and embed lessons into future cost estimation. This study's objective is to explore how learning from previous projects can improve the accuracy of cost estimation, by analyzing current practices, identifying barriers and enablers, and recommending strategies. Drawing on 23 interviews in the Dutch road sector, the research identifies time pressure, leadership priorities, and fragmented responsibilities as key barriers. Teams consistently prioritize preparing new bids over evaluating completed work, leaving little room for structured reflection. Revenue targets and skilled personnel shortages further reduce the time and capacity available for learning. While an open and collaborative team culture enables informal knowledge sharing, such exchanges rarely extend beyond individual projects. The study examines how leadership influences this dynamic, finding that while managers express support for learning, operational pressures often override reflection. Leaming remains spontaneous unless visibly prioritized & structurally planned. To analyze where and how learning breaks down, the paper applies the multi-level learning framework for project-based organizations (PBO's) treating projects as temporary organizations embedded in a wider coordinating structure. Based on this lens, the study introduces a seventh learning process; "Iterating", to capture dynamic loops of reflection, adjustment, and knowledge integration during project execution. The findings offer insight into what it takes to institutionalize learning in fast-paced project environments: leadership that creates space for reflection, routines that embed feedback into project delivery, and cultural trust that enables open exchange.